M -plane (101̱0) InN heteroepitaxied on (100)-γ-LiAlO2 substrate: Growth orientation control and characterization of structural and optical anisotropy

Abstract

Heteroepitaxial growth of m-plane (101̱0) InN film on (100)-γ-LiAlO2 (LAO) substrate has been realized by plasma-assisted molecular-beam epitaxy. Surface treatment of LAO substrate plays an important role in controlling the resultant phase and purity of m-plane InN. X-ray diffraction, reflection high-energy electron diffraction, electron back scatter diffraction, and transmission electron microscopy (TEM) studies revealed formation of pure m-plane InN film using substrate preannealed at 800 °C but without any nitridation. In contrast, using substrate with nitridation but otherwise identical pretreatment and growth conditions, c-plane (0001) InN columnar structure was grown, instead of m-plane InN film. Structural anisotropy of the m-plane InN epitaxied on LAO is attributed to the I1 type base-plane stacking faults according to the modified Williamson–Hall and TEM analyses. A rectangular-to-rectangular atomic stacking sequence and a commensurately lattice-matched condition in epitaxial direction of [12̱10]InN∥[001]LAO with a small misfit strain of ∼0.2% are proposed to realize this heteroepitaxy. Angle-dependent polarized UV-Raman spectra showed that all the InN phonon modes follow Raman selection rule well. Strong polarization anisotropy of photoluminescence (PL) emission located at ∼0.63 eV was observed, as evidenced by a high polarization degree of 87% of the m-plane InN determined by infrared polarized PL spectroscopy.